The present invention relates generally to a method of manufacturing a semiconductor device using a fluorine-containing layer, such as a fluorine-containing carbon layer, as an insulating layer.
In the recent semiconductor integrated circuit producing industry, technical developments, such as the scale down of wiring patterns and the multilayering of wiring, have been made in order to achieve the high density integration. For example, in the wiring multilayering technique, there is used a wiring structure wherein a plurality of wiring layers are stacked via interlayer dielectric films and wherein adjacent two of the wiring layers are connected to each other by a conductive portion arranged in a through hole formed in each of the interlayer dielectric films.
In this case, a silicon oxide (SiO2) film capable of being easily formed on a silicon substrate, which comes into widest use as a semiconductor substrate, is generally used as the interlayer dielectric film. However, SiO2 has a relatively large relative dielectric constant ∈ of about 4, which is an obstacle to develop more rapid semiconductor integrated circuits.
In order to solve such a problem, there is proposed a fluorine-containing carbon film which has a smaller relative dielectric constant than that of SiO2 and which comprises carbon (C) and fluorine (F). The fluorine-containing carbon film can be formed by a plasma process using the electron cyclotron resonance (ECR).
This film-forming method will be described. First, a film-forming system shown in FIG. 3 is used. This film-forming system comprises a plasma producing chamber 501a of manufacturing plasma, and a film-forming chamber 501b communicated therewith. A microwave of 2.45 GHz is supplied to the plasma producing chamber 501a from a high-frequency power supply unit 502 via a waveguide 502a to produce plasma. In the film-forming chamber 501b, a supporting table 506 is arranged, and a wafer 507 to be processed is fixed thereon by an electrostatic chuck 506a. The interior of each of the plasma producing chamber 501a and film-forming chamber 501b is evacuated to a predetermined degree of vacuum by an evacuating means (not shown) which is communicated thereto via an exhaust pipe 510.
Such a film-forming system is used for forming a fluorine-containing carbon film on the wafer 507 as follows. First, the microwave of 2.45 GHz is supplied to the plasma producing chamber 501a from the high-frequency power supply unit 502 via the waveguide 502a. Then, together therewith, a magnetic field of 875 gausses is applied by magnetic coils 503 and 503a to activate argon (Ar) gas, which has been introduced from an introducing pipe 504, by the electron cyclotron resonance to be high-density plasma. On the other hand, C4F8 and C2H4 gases are introduced into the film-forming chamber 501b from a gas supply part 505 via gas introducing pipes 505a and 505b to activate these gases by the high density plasma to form active species (radicals and so forth). Then, by the active species, a fluorine-containing carbon film 508 having good adhesion and high hardness is formed on the wafer 507 which is fixed on the supporting table 506 arranged in the film-forming chamber 501b. 
By the way, as described above, in order to construct a semiconductor device, upper and lower wiring layers are connected to each other by the conductive portion, which is arranged in a through hole formed in an interlayer dielectric film, so that it is required to carry out a fine pattern process, such as the formation of a through hole in an interlayer dielectric film. Thus, it is necessary to carry out a fine pattern process, such as the formation of a through hole in the fluorine-containing carbon film used as an interlayer dielectric film.
However, the fluorine-containing carbon film is an organic material, so that the patterning technique for an SiO2 film which is an inorganic film can not be used as it is. The reason for this is as follows. First, in the fine pattern process, a resist pattern having formed generally by the photolithography technique is used as a mask to carry out a selective etching. At this time, the resist pattern must have an etching resistance as a mask against an underlying layer to be patterned. If the layer to be patterned is thick, the etching resistance of the resist pattern is particularly required. This resist pattern is formed by, e.g., exposing and developing a photoresist having photosensitivity, and is made of an organic material.
However, when an organic film, such as the above described fluorine-containing carbon film, is fine-patterned, a dry etching using the plasma of oxygen gas (O2) is used. In this case, if the resist pattern being the organic film is used as a mask, the resist pattern is also etched, so that it is not possible to carry out any selective etching processes. Thus, if the photoresist is used as a master pattern as conventional methods, it is not possible to carry out any selective etching processes, and the master pattern is also etched. Therefore, the dimension of the master pattern and so forth vary, so that it is not possible to precisely fine-pattern the fluorine-containing carbon film.
On the other hand, if a master pattern of an inorganic insulating material, such as SiO2, is used when the fluorine-containing carbon film is etched with the plasma of O2, the master pattern is hardly etched with the plasma of O2. Therefore, it is possible to carry out a selective etching, so that it is possible to carry out a fine pattern process while maintaining a high dimensional precision.
For that reason, in the fine pattern process of the fluorine-containing carbon film, a hard mask of SiO2 or the like is used. If the hard mask is made of an inorganic insulating material, it is possible to obtain a high etch selectivity to the fluorine-containing carbon film, so that the hard mask may be thin.
Therefore, if the fluorine-containing carbon film is used as the interlayer dielectric film, there is no problem from the point of view of insulation performance even if the hard mask remains, and there is no serious problem with respect to the relative dielectric constant if the thickness is small. For that reason, if the fluorine-containing carbon film is used as the interlayer dielectric film, the hard mask having used for the pattern lithography is designed to remain without being removed, since the number of steps increases if the hard mask is removed.
The fine pattern process of the fluorine-containing carbon film using such a hard mask will be described below.
First, as shown in FIG. 4(a), a fluorine-containing carbon film 602 is formed on a bottom wiring layer 601 serving as a substrate as described above. Then, an inorganic insulating film 603 of SiO2 is formed on the fluorine-containing carbon film 602 by a chemical vapor deposition (CVD) method using SiH4 or the like as a raw material, which is a well-known technique. The silicon (Si) containing inorganic insulating layer, such as SiO2, is a generally used insulating material since it has good adhesion to metallic materials used as materials of wiring layers and since its raw material is inexpensive and its deposition technique is established so that it can be easily handled.
Then, as shown in FIG. 4(b), a resist pattern 604 having an opening portion 604a at a predetermined position is formed on the inorganic insulating film 603 by a well-known photolithography technique.
Then, the resist pattern 604 is used as a mask for selectively etching the inorganic insulating film 603. Thus, as shown in FIG. 4(c), a hard mask 605 having an opening portion 605a at a position corresponding to the opening portion 604a is formed. In this etching, a dry etching using, e.g., the plasma of CF4 or C3F8, may be used.
Then, the hard mask 605 is used as a mask for selectively etching the fluorine-containing carbon film 602. Thus, as shown in FIG. 4(d), a hole portion 606 is formed in the fluorine-containing carbon film 602. In this etching, a dry etching using, e.g., the plasma of O2, may be used. As described above, if O2 is used, it is possible to obtain a high etch selectivity (a ratio of etch rates) between the fluorine-containing carbon film 602 and the hard mask 605. If the plasma of O2 is used, the resist pattern 602 can be simultaneously etched and removed.
However, if the hard mask of SiO2 or silicon nitride (SiN), which is generally used for patterning organic films, is caused to remain after being used for the fine pattern lithography of the fluorine-containing carbon film, there is a problem in that the adhesion of the hard mask to the upper and lower layers deteriorates with age so as to lower the reliability of the semiconductor device using the fluorine-containing carbon film as the insulating layer. For example, even if the adhesion is maintained during the pattern lithography using the hard mask, peeling occurs in the hard mask portion after the semiconductor device is completed, so that a failure is caused in the semiconductor device.
The present invention has been made in order to eliminate the above described problems. That is, it is an object of the present invention to provide a method of manufacturing a semiconductor device, which can improve the reliability of the semiconductor device having a structure wherein a fluorine-containing insulating layer, such as a fluorine-containing carbon film, is adjacent to a silicon containing insulating layer serving as a hard mask.
In order to accomplish this object, according to one aspect of the present invention, there is provided a method of manufacturing a semiconductor device comprising the steps of: forming a wiring layer on a semiconductor substrate, on which an element has been formed; forming a first insulating layer containing fluorine on the wiring layer; forming a second insulating layer containing silicon on the first insulating layer; selectively etching the second insulating layer until a part of a surface of the first insulating layer is exposed; selectively etching the first insulating layer using the selectively etched second insulating layer as a mask; and forming a new wiring layer on the second insulating layer after selectively etching the first insulating layer, wherein a silicon compound containing no hydrogen is used as a raw material of silicon constituting the second insulating layer at the step of forming the second insulating layer.
If the silicon compound containing no hydrogen is thus used as the raw material of silicon constituting the second insulating layer at the step of forming the second insulating layer, hydrogen is inhibited from being incorporated into the formed second insulating layer, so that hydrogen is also inhibited from being degassed from the formed second insulating layer. Therefore, hydrogen having diffused outwardly from the second insulating layer to the first insulating layer is inhibited from being bonded to fluorine in the first insulating layer to form HF. As a result, the corrosion of the second insulating layer with HF is inhibited, so that the deterioration of the adhesion of the second insulating layer to other layers is inhibited. Therefore, according to the present invention, it is possible to improve the reliability of a semiconductor device having a structure wherein a fluorine-containing insulating layer is adjacent to a silicon containing insulating layer.
If a substance containing no hydrogen is used as a raw material of a substance other than silicon constituting the second insulating layer at the step of the second insulating layer, hydrogen is further inhibited from being incorporated into the second insulating layer.
The step of forming the second insulating layer may be carried out by a chemical vapor deposition process or a sputtering process. In the latter sputtering process, if the plasma of a gas containing no hydrogen is used, hydrogen is further inhibited from being incorporated into the second insulating layer.